Variation in the development of cadmium resistance in Daphnia magna straus; effect of temperature, nutrition, age and genotype

The extent to which responses to toxicants can be modified by the environment and genotype of Daphnia magna is important for interpreting the results from ecotoxicity tests. Variation in the development of cadmium resistance and its relevance for survivorship has been investigated in two genetically distinct clones of D. magna. Cadmium resistance was induced by pre-exposing daphnids to a sublethal concentration of a Cd/Zn mixture and thereafter cadmium tolerance was assessed in standard acute tests. The results showed that the ability to develop cadmium resistance is affected by temperature, but there is no consistent pattern for maternal nutrition. The age of the daphnids had no apparent effect on the development of cadmium resistance. Differences in the induction of cadmium resistance between clones were seen only under resource depression.     

The use of the cotton-strip assay to assess cellulose decomposition in heavy metal-contaminated sewage sludge-amended soils

Cellulose decomposition in soils amended over twenty year ago with heavy metal-contaminated sewage sludges was assessed by using the cotton-strip assay. The soils of the Luddington Experiment now contain concentrations of Cu, Ni and Zn in selected plots that approximate to or exceed the statutory limits for these elements in sewage sludge-amended soils. The rates of cellulose decomposition were generally lower in the plots with elevated metal concentrations, relative to uncontaminated sludge-amended and unsludged controls. Generally, the metal-rich plots showed reductions in the time taken to reach 50% cotton-tensile-strength loss (CTSL). However, the reductions could not be consistently related to any one metal. The difference in decomposition rates between treatments was systematically reduced over the duration of a time-course experiment. A lower initial population of the appropriate decomposer community of micro-organisms may account for the observed short-term lag in decomposition rates.     

Regional concentration levels of vanadium, aluminium and bromine in mosses and lichens

Concentrations of V, Al and Br determined by neutron activation analysis showed significant interspecies differences: the epiphytic lichen had consistently higher elemental concentrations than the peat moss or the terricolous lichen collected from the same sites. A regional survey with the latter two species indicated a distinct decrease of V and Al levels from south to north Finland. A large-scale survey with mosses showed relatively low levels of vanadium in remote areas of Scandinavia, but somewhat elevated concentrations of V e.g. in samples from Leningrad region, northern Germany, Wales and northeastern U.S.A.     

The fate of chlorobenzenes and permethrins during anaerobic sewage sludge digestion

Mixed primary sewage sludge was incubated anaerobically with and without azide addition to prevent biological activity. The behaviour of 1,3-, 1,4- and 1,2-dichlorobenzene, 1,3,5-, 1,2,4- and 1,2,3-trichlorobenzene, 1,2,3,4- and 1,2,4,5-tetrachlorobenzene, hexachlorobenzene, and cis- and trans-permethrin was examined to determine their potential removal during anaerobic digestion. All the chlorobenzenes were removed to varying extents over 32 days of incubation, ranging from 25% removal for 1,3,5-trichlorobenzene to 80% removal for 1,4-dichlorobenzene. Biodegradation may have been responsible for the reductions in 1,3- and 1,4-dichlorobenzene and 1,2,4- and 1,2,3-trichlorobenzene as there was no significant removal of these compounds in azide treated sludge. The removal over 32 days of cis- and transpermethrin was 87% and 96% respectively. These removals were attributed to a chemical or physical process.     

Loss of HCH from surface soil layers under subtropical conditions

The loss of HCH (hexachlorocyclohexane) at an application rate of 25 kg ha(-1) was studied under field conditions from two surface soil layers, each of 7.5 cm, at two sites in Delhi. The soil at both sites was sandy loam type, with a pH of 8.2, and 0.8 to 1.0% organic matter content. At site 1, which was kept fallow and not watered, the upper 7.5-cm layer of soil initially lost HCH more rapidly than the lower layer. The half-life of the HCH in the upper and lower 7.5-cm layers was 21 and 41 days, respectively, and it was 26 days for the total HCH in the combined 15-cm soil layer. At site 2, which contained ornamental plants and was watered regularly, there was not much difference in the loss of HCH between the upper and lower layers. The half-life of HCH was 17 and 25 days for the upper and lower 7.5-cm layers, respectively, and it was 20 days for the total 15-cm soil layer, at this site. The loss was greatest initially at the sites, and was faster in wet soil than in dry soil.     

Ozone-induced changes in CO2 assimilation, O2 evolution and chlorophyll a fluorescence transients in barley

Spring barley (Hordeum vulgare cv. Klaxon) plants, 9 days old, were exposed to 0.05, 0.10 or 0.15 microl litre(-1) ozone (O3) for 12 days. Fumigation was administered for 7 h between 9.00 h and 16.00 h each day. Using conventional IRGA equipment, the carbon dioxide exchange rate (CER) was shown to decrease with increasing concentration of O3 during the exposure period, falling to 60% of the control value at the highest O3 concentration. Transpiration rates and stomatal conductance showed similar trends. Light saturation curves, obtained using a leaf disc oxygen electrode, demonstrated that O3-treated leaves had lower apparent quantum yields (QY) and generally lower rates of O2 evolution at saturating light and CO2 levels. Oscillations in chlorophyll a fluorescence, normally observed in control plants, could not be detected after O3 treatment and could only be restored to some extent by feeding the phosphate sequestering agent D-mannose to the leaves.     

Oxidant air pollution effects on plants of Joshua Tree National Monument

Joshua Tree National Monument (JOTR) is located about 100 km east of the Los Angeles Basin, site of the heaviest concentration of photochemical oxidant (O(3)) air pollution in the US. This investigation was conducted to measure O(3) concentrations in JOTR and to determine the effects of O(3) on vegetation in the park. Potentially phytotoxic concentrations of O(3) were recorded in JOTR in 1984 and 1985, but peak concentration occurred at night, when most plant species would be less sensitive to O(3). No O(3) effects were observed on permanent vegetation observation plots in JOTR in 1984 or 1985. Controlled exposures of native summer annual and woody perennial species to O(3) showed that most did not develop visible O(3) injury symptoms except at concentrations higher than those expected in the park. However, Rhus trilobata Nutt. was injured at 0.10 ppm O(3), 4 h per day for 4 days. This species would be a useful bioindicator to assess the effects of O(3) on native desert plants.     

Selecting ozone exposure statistics for determining crop yield loss from air pollutants

Numerous ozone exposure statistics were calculated using hourly ozone data from crop yield loss experiments previously conducted for alfalfa, fresh market and processing tomatoes, cotton, and dry beans in an ambient ozone gradient near Los Angeles, California. Exposure statistics examined included peak (maximum daily hourly) and mean concentrations above specific threshold levels, and concentrations during specific time periods of the day. Peak and mean statistics weighted for ozone concentration and time period statistics weighted for hour of the day were also determined. Polynomial regression analysis was used to relate each of 163 ozone statistics to crop yield. Performance of the various statistics was rated by comparing residual mean square (RMS) values. The analyses demonstrated that no single statistic was best for all crop species. Ozone statistics with a threshold level performed well for most crops, but optimum threshold level was dependent upon crop species and varied with the particular statistics calculated. The data indicated that daily hours of exposure above a critical high-concentration threshold related well to crop yield for alfalfa, market tomatoes, and dry beans. The best statistic for cotton yield was an average of all daily peak ozone concentrations. Several different types of ozone statistics performed similarly for processing tomatoes. These analyses suggest that several ozone summary statistics should be examined in assessing the relationship of ambient ozone exposure to crop yield. Where no clear statistical preference is indicated among several statistics, those most biologically relevant should be selected.